Physics in Your World

Notice that both the ant and the small image of the flower are in focus in this photograph (high-res version)--therefore, both must be at approximately the same distance from the camera lens. Since a drop of water has a small radius of curvature, its focal length is short, only about half a centimeter, so the image is close to the drop and is much smaller than the flower itself.

Physics at Home

To do a simple experiment with a convex lens, go to Exploratorium: Snacks About Light, scroll down to the bottom of the list of activities, and click on "Water Sphere Lens." Try using a fishbowl of water as a lens. You can do the same activity with a magnifying glass, but be sure NOT to look through the magnifying glass into a bright light, or into the sun.

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From Physics Research

This photo (hi-res image) shows the moon, looking along the 40-inch refracting telescope at the Yerkes Observatory. Its focal length is long--about 19 meters--so the real image it makes will be big. This is the world's largest refractor.